s3 8p, exhaust giving out burning oil smell, no smoke.

I have an s3 8p with an issue where when i come to a stop and have either the window down or heating/air con on i get a bad smell of burning oil yet the car doesnt smoke... putting my nose near the exhaust tips (of course with the car off) i can smell it, its 100% from the exhaust, oil consumption is 1l between 1000-2000 miles.

i do have a decat but it hasnt always smelt like this.